This application is based on Japanese Patent Application No. 9-329210, filed Nov. 28, 1997, the content of which is incorporated herein by reference.
The present invention relates to a computer system and a system state control method and, more particularly, to a computer system having ON and OFF states and a plurality of sleep states between them as system states, and a system state control method for changing the system state.
Various battery drivable personal computers represented by a notebook type computer have recently been developed. In personal computers of this type, power management techniques have been studied for low power consumption and a short ON state return time. One of these techniques is ACPI (Advanced Configuration and Power Interface) specifications.
The ACPI specifications define ON and OFF states, and in addition a plurality of sleep states between them as system states.
More specifically, the ACPI specifications define system states S0 through S5. S0 is an ON state (i.e., the system is turned on, and software is in process). S5 is an OFF state (i.e., execution of all software is complete, and the system is turned off). S1 through S4 are intermediate states (called sleep states; i.e., the preceding execution state of software is maintained, but the operation stops).
In S1, the contents (contexts) of all the components (e.g., CPU, system memory, and chip sets) of the system, and their power supplies are maintained, and thus the power consumption is maximum of all the sleep states. However, S1 can immediately return to S0. That is, S0 is the "lightest" sleep state. Note that the light sleep state cannot be maintained for a long time in the battery-driven state of a notebook type personal computer or the like.
S2 is different from S1 in that the power supplies of the CPU and the system cache are turned off (and their contents are lost). The necessary power consumption is therefore reduced.
In S3, the power supply of only the system memory (and some chip sets) is maintained. That is, the contents of only the system memory (and some chip sets) are maintained. The necessary power supply is much smaller, so that the sleep state can be maintained for a long time in the battery-driven state.
In S4, the contents of all the system memory and other components are stored in a non-volatile storage such as a hard disk, and the system power supply is entirely turned off. The power consumption is minimum (equal to S5) of all the sleep states, but it takes the longest time to return to S0. That is, S4 is the "deepest" sleep state.
In return to S0 from S2 through S4, the lost contents in the system are restored because they are stored before transition to each sleep state. Therefore, upon return to S0, software can continuously operate.
The power consumption relationship between the system states, and the relationship of the return time to S0 are as follows:
Power Consumption: S0&gt;S1&gt;S2&gt;S3&gt;S4&gt;S5
Return Time: S1&lt;S2&lt;S3&lt;S4&lt;S5
However, in the current ACPI specifications, no consideration is made to change the depth of the sleep state in accordance with a change in power supply state during sleep. For example, a battery-driven notebook type PC cannot change to such an appropriate sleep state as to minimize the battery consumption. When the battery changes to a low battery state (current sleep state cannot be maintained) in a light sleep state, the sleep state cannot change to a deeper sleep state.